getsockopt, setsockopt - get and set options on sockets


cc [ flag ... ] file ... -lsocket -lnsl [ library ... ]
#include <sys/types.h>
#include <sys/socket.h>

int getsockopt(int s, int level, int optname, void *optval,
int *optlen);

int setsockopt(int s, int level, int optname, const void *optval,
int optlen);


The getsockopt() and setsockopt() functions manipulate options associated
with a socket. Options may exist at multiple protocol levels; they are
always present at the uppermost "socket" level.

The level argument specifies the protocol level at which the option
resides. To manipulate options at the socket level, specify the level
argument as SOL_SOCKET. To manipulate options at the protocol level,
supply the appropriate protocol number for the protocol controlling the
option. For example, to indicate that an option will be interpreted by
the TCP, set level to the protocol number of TCP, as defined in the
<netinet/in.h> header, or as determined by using getprotobyname(3SOCKET).
Some socket protocol families may also define additional levels, such as
SOL_ROUTE. Only socket-level options are described here.

The parameters optval and optlen are used to access option values for
setsockopt(). For getsockopt(), they identify a buffer in which the
value(s) for the requested option(s) are to be returned. For
getsockopt(), optlen is a value-result parameter, initially containing
the size of the buffer pointed to by optval, and modified on return to
indicate the actual size of the value returned. Use a 0 optval if no
option value is to be supplied or returned.

The optname and any specified options are passed uninterpreted to the
appropriate protocol module for interpretation. The include file
<sys/socket.h> contains definitions for the socket-level options
described below. Options at other protocol levels vary in format and

Most socket-level options take an int for optval. For setsockopt(), the
optval parameter should be non-zero to enable a boolean option, or zero
if the option is to be disabled. SO_LINGER uses a struct linger parameter
that specifies the desired state of the option and the linger interval.
struct linger is defined in <sys/socket.h>. struct linger contains the
following members:

on = 1/off = 0

linger time, in seconds

The following options are recognized at the socket level. Except as
noted, each may be examined with getsockopt() and set with setsockopt().

enable/disable recording of debugging information

enable/disable local address reuse

enable/disable keep connections alive

enable/disable routing bypass for outgoing messages

linger on close if data is present

enable/disable permission to transmit broadcast

enable/disable reception of out-of-band data in band

set buffer size for output

set buffer size for input

application wants delayed error

enable/disable reception of timestamp with datagrams

enable/disable exclusive binding of the socket

get the type of the socket (get only)

get and clear error on the socket (get only)

get or set mandatory access control on the socket.
This option is available only when the system is
configured with Trusted Extensions.

bypass zone boundaries (privileged).

get the domain used in the socket (get only)

for socket in domains PF_INET and PF_INET6, get the
underlying protocol number used in the socket. For
socket in domain PF_ROUTE, get the address family used
in the socket.

The SO_DEBUG option enables debugging in the underlying protocol modules.
The SO_REUSEADDR option indicates that the rules used in validating
addresses supplied in a bind(3SOCKET) call should allow reuse of local
addresses. The SO_KEEPALIVE option enables the periodic transmission of
messages on a connected socket. If the connected party fails to respond
to these messages, the connection is considered broken and threads using
the socket are notified using a SIGPIPE signal. The SO_DONTROUTE option
indicates that outgoing messages should bypass the standard routing
facilities. Instead, messages are directed to the appropriate network
interface according to the network portion of the destination address.

The SO_LINGER option controls the action taken when unsent messages are
queued on a socket and a close(2) is performed. If the socket promises
reliable delivery of data and SO_LINGER is set, the system will block the
thread on the close() attempt until it is able to transmit the data or
until it decides it is unable to deliver the information (a timeout
period, termed the linger interval, is specified in the setsockopt() call
when SO_LINGER is requested). If SO_LINGER is disabled and a close() is
issued, the system will process the close() in a manner that allows the
thread to continue as quickly as possible.

The option SO_BROADCAST requests permission to send broadcast datagrams
on the socket. With protocols that support out-of-band data, the
SO_OOBINLINE option requests that out-of-band data be placed in the
normal data input queue as received; it will then be accessible with
recv() or read() calls without the MSG_OOB flag.

The SO_SNDBUF and SO_RCVBUF options adjust the normal buffer sizes
allocated for output and input buffers, respectively. The buffer size may
be increased for high-volume connections or may be decreased to limit the
possible backlog of incoming data. The maximum buffer size for UDP is
determined by the value of the ndd variable udp_max_buf. The maximum
buffer size for TCP is determined the value of the ndd variable
tcp_max_buf. Use the ndd(8) utility to determine the current default
values. See the Solaris Tunable Parameters Reference Manual for
information on setting the values of udp_max_buf and tcp_max_buf. At
present, lowering SO_RCVBUF on a TCP connection after it has been
established has no effect.

By default, delayed errors (such as ICMP port unreachable packets) are
returned only for connected datagram sockets. The SO_DGRAM_ERRIND option
makes it possible to receive errors for datagram sockets that are not
connected. When this option is set, certain delayed errors received after
completion of a sendto() or sendmsg() operation will cause a subsequent
sendto() or sendmsg() operation using the same destination address (to
parameter) to fail with the appropriate error. See send(3SOCKET).

If the SO_TIMESTAMP option is enabled on a SO_DGRAM or a SO_RAW socket,
the recvmsg(3XNET) call will return a timestamp in the native data
format, corresponding to when the datagram was received.

The SO_EXCLBIND option is used to enable or disable the exclusive binding
of a socket. It overrides the use of the SO_REUSEADDR option to reuse an
address on bind(3SOCKET). The actual semantics of the SO_EXCLBIND option
depend on the underlying protocol. See tcp(4P) or udp(4P) for more

The SO_TYPE and SO_ERROR options are used only with getsockopt(). The
SO_TYPE option returns the type of the socket, for example, SOCK_STREAM.
It is useful for servers that inherit sockets on startup. The SO_ERROR
option returns any pending error on the socket and clears the error
status. It may be used to check for asynchronous errors on connected
datagram sockets or for other asynchronous errors.

The SO_MAC_EXEMPT option is used to toggle socket behavior with unlabeled
peers. A socket that has this option enabled can communicate with an
unlabeled peer if it is in the global zone or has a label that dominates
the default label of the peer. Otherwise, the socket must have a label
that is equal to the default label of the unlabeled peer. Calling
setsockopt() with this option returns an EACCES error if the process
lacks the NET_MAC_AWARE privilege or if the socket is bound. The
SO_MAC_EXEMPT option is available only when the system is configured with
Trusted Extensions.

The SO_ALLZONES option can be used to bypass zone boundaries between
shared-IP zones. Normally, the system prevents a socket from being bound
to an address that is not assigned to the current zone. It also prevents
a socket that is bound to a wildcard address from receiving traffic for
other zones. However, some daemons which run in the global zone might
need to send and receive traffic using addresses that belong to other
shared-IP zones. If set before a socket is bound, SO_ALLZONES causes the
socket to ignore zone boundaries between shared-IP zones and permits the
socket to be bound to any address assigned to the shared-IP zones. If the
socket is bound to a wildcard address, it receives traffic intended for
all shared-IP zones and behaves as if an equivalent socket were bound in
each active shared-IP zone. Applications that use the SO_ALLZONES option
to initiate connections or send datagram traffic should specify the
source address for outbound traffic by binding to a specific address.
There is no effect from setting this option in an exclusive-IP zone.
Setting this option requires the sys_net_config privilege. See zones(7).


If successful, getsockopt() and setsockopt() return 0. Otherwise, the
functions return -1 and set errno to indicate the error.


The getsockopt() and setsockopt() calls succeed unless:

The argument s is not a valid file descriptor.

There was insufficient memory available for the
operation to complete.

The option is unknown at the level indicated.

There were insufficient STREAMS resources available for
the operation to complete.

The argument s is not a socket.

SO_SNDBUF or SO_RCVBUF exceeds a system limit.

Invalid length for a given socket option.

Invalid address for IP_MULTICAST_IF.

Not a multicast address for IP_ADD_MEMBERSHIP and

Bad interface address for IP_ADD_MEMBERSHIP and

Address already joined for IP_ADD_MEMBERSHIP.

Address not joined for IP_DROP_MEMBERSHIP.

No permissions.

Permission denied.

The specified option is invalid at the specified socket
level, or the socket has been shut down.


See attributes(7) for descriptions of the following attributes:

|MT-Level | Safe |


close(2), ioctl(2), read(2), socket.h(3HEAD), bind(3SOCKET),
getprotobyname(3SOCKET), recv(3SOCKET), send(3SOCKET), socket(3SOCKET),
recvmsg(3XNET), tcp(4P), udp(4P), attributes(7), zones(7), ndd(8)

Solaris Tunable Parameters Reference Manual

January 27, 2009 GETSOCKOPT(3SOCKET)